1. Field of the Invention
This invention generally relates to a clutch drum. More specifically, the present invention relates to a clutch drum for a multiple plate clutch that houses a plurality of clutch plates.
2. Background Information
The transmissions used in automatic automobiles are often equipped with multiple plate wet clutches. Multiple plate clutches are typically equipped with a clutch drum, a piston, a plurality of drive plates, a plurality of driven plates, and an output member. The clutch drum is a cylindrical member, with one end open and the other end substantially closed. The clutch drum is fixedly coupled to an input shaft which receives torque from the engine. The piston is arranged so that it can move freely in the axial direction within the clutch drum. The drive plates and the driven plates are arranged within the clutch drum so as to alternate in the axial direction. The drive plates mate with the inside circumferential surface of the clutch drum in such a manner that they can move freely in the axial direction but cannot undergo relative rotation. The driven plates mate with the outside surface of the output member in such a manner that they can move freely in the axial direction but cannot undergo relative rotation.
With this kind of multiple plate clutch, when the clutch is engaged, hydraulic pressure is supplied to the piston to move the piston in the axial direction by the operating fluid. As a result, the drive plates and the driven plates are pressed together by the piston. Thus, the drive plates and, the driven plates can rotate as a single unit and the torque from the engine is transmitted to the transmission. Specifically, the torque from the engine is transmitted to the transmission through the following components in order as listed: the input shaft, the clutch drum, the drive plates, the driven plates, and the output member.
The clutch drum in this type of multiple plate clutch generally has a cylindrical part with a plurality of teeth formed on the inside of the cylindrical part. The plurality of teeth mate with the outside of the drive plates. The drive plates can move freely in the axial direction but cannot rotate with respect to the cylindrical part.
Since the plurality of teeth in this kind of clutch drum are formed so as to project inward from the inside of the cylindrical part, the drum is thicker at the locations where the teeth are formed. Consequently, the overall weight of the clutch drum increases according to the weight of the teeth. A heavy clutch drum can cause trouble during shifting because more time is required for stopping rotation of the clutch drum.
In order to resolve this problem, clutch drums have already been proposed which attempt to reduce the weight by eliminating all material except for material that forms the faces of the plurality of teeth, as shown in FIGS. 4 and 5.
As shown in FIG. 4, the clutch drum 15xe2x80x2 is deeply recessed at the outside part of tooth 25xe2x80x2. Although the weight of the clutch drum 15xe2x80x2 has been reduced, the mechanical losses are large because the agitation resistance between the drum and the operating fluid disposed on the outside thereof increases when the clutch drum 15xe2x80x2 rotates.
On the other hand, as shown in FIG. 5, the overall weight of the clutch drum 15xe2x80x3 is also reduced when only the tooth flanks are formed in the clutch drum 15xe2x80x3. However, the mechanical strength of the clutch drum 15xe2x80x3 is reduced because the majority of each tooth 25xe2x80x3 is formed by thin walled projections. More specifically, sufficient strength cannot be secured against the stresses imposed by the drive plates in the rotational direction.
In, view of the above, there exists a need for a clutch drum which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
An object of the present invention is to provide a clutch drum in which the weight of the clutch drum is reduced, while maintaining the mechanical losses of the clutch drum in check.
The forgoing object of the present invention can be attained by a clutch drum that houses a plurality of clutch plates. The clutch drum includes cylindrical part and a plurality of teeth that are arranged circumferentially around the inside of the cylindrical part and extend in the axial direction. The plurality of teeth have an inner circumferential surface as well as tooth flanks on both sides in the rotational direction and the cylindrical part has bottom lands formed on its inner surface between the plurality of teeth in the rotational direction. The first recesses are formed on the portions of the outside surface of the cylindrical part that correspond to the plurality of teeth and second recesses are formed on the inside surfaces of the plurality of teeth.
With this clutch drum, when the clutch is engaged, the plurality of clutch plates move in the axial direction guided by the plurality of teeth and press against one another. As a result, torque can be transmitted between the plurality of clutch plates. Also, the plurality of teeth have more wall thickness than in conventional clutch drums because first recesses and second recesses corresponding to each of the plurality of teeth are formed in the outside surface and inside surface of the cylindrical part.
Here, since recesses are formed in both the outside surface and the inside surface of the cylindrical part, the desired weight reduction can be achieved even if the first and second recesses are each relatively small. Furthermore, the mechanical losses at the outside surface of the cylindrical part can be reduced and sufficient mechanical strength can be obtained for the clutch drum at the inside surface of the cylindrical part.
In accordance with another aspect of the present invention, the clutch drum described above preferably has the second recesses b formed so as to blend smoothly with the inside surfaces of the teeth. Here, sufficient mechanical strength is secured for the clutch drum because the wall thickness of the teeth varies smoothly in the circumferential direction.
In accordance with another aspect of the present invention, the first recesses are preferably formed so as to blend smoothly with the outside surface of the cylindrical part. Here, the agitation resistance between the outside surface of the cylindrical part and the operating fluid is lowered and mechanical losses can be reduced.
In accordance with another aspect of the present invention, the shortest distance between the first recess and a circumferential edge of the inside surface of the plurality of teeth is longer than the shortest distance between the first recess and the second recess.
In accordance with another aspect of the present invention, a reference cross sectional area S is defined as the surface area of a cross section demarcated by an outside arc that links the bottom lands in the circumferential direction, an inside arc that links the innermost edges of the plurality of teeth in the circumferential direction, and the lines obtained by extending the tooth flanks of each tooth; cross sectional area S1 is defined as the surface area of a cross section demarcated by the first recess and the outside arc; and the ratio of cross sectional area S1 to reference cross sectional area S is greater than or equal to 0.05 and less than or equal to 0.40 for each tooth.
In accordance with another aspect of the present invention, a reference cross sectional area S is defined as the surface area of a cross section demarcated by an outside arc that links the bottom lands in the circumferential direction, an inside arc that links the innermost edges of the plurality of teeth in the circumferential direction, and the lines obtained by extending the tooth flanks of each tooth; cross sectional area S2 is defined as the surface area of a cross section demarcated by the second recess and the inside arc; and the ratio of cross sectional area S2 to reference cross sectional area S is greater than or equal to 0.05 and less than or equal to 0.30 for each tooth.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.